Inductive proximity sensors commonly exhibit hysteresis. That is, they are triggered when an approaching conductive object crosses a known point in space, but they are not detriggered until the object reverses its approach and withdraws to a detrigger point farther away than the trigger point. That is, such sensors, once triggered, do not detect motion of the object within a region termed a hysteresis region located between the two points.
This causes problems when such sensors are used to ascertain the positioning of an object because they allow the object to move undetected within the hysteresis region. In some situations, greater detective precision than this is needed. For example, when a workpiece is clamped into a vise for a machining operation, and if such a sensor is used to ascertain whether the workpiece is positioned correctly, movement of the workpiece following triggering of the sensor may not be detected, resulting in faulty positioning. The problem is worsened when automated equipment is used because a human operator generally is not present to supervise the positioning of each workpiece. Accurate positioning of workpieces in fixtures is important in the gas turbine engine industry.